Maintenance of glucose homeostasis is central to our health, and its failure results in severe debilitating diseases including diabetes and familial hyperinsulinism. Diabetes mellitus is a metabolic disorder that affects over 285 million people worldwide and is a leading cause of death in many countries. The disease is characterized by either absolute insulin deficiency due to the autoimmune destruction of pancreatic insulin-producing ?-cells [Type 1 diabetes mellitus (T1DM)], or relative insulin deficiency due to defective insulin secretion or insulin sensitivity [Type 2 diabetes mellitus (T2DM)]. The resulting elevated blood glucose levels eventually lead to an impairment of the microvasculature followed by kidney failure, blindness, neuropathy and heart disease. Consequently, diabetes is currently the sixth leading cause of death in the United States (CDC). During the past grant cycle, we have made the exciting discovery that the imprinted MEG3 locus is strongly down-regulated in islets from type 2 diabetics. The MEG3 locus is of particular interest in that it encodes a cluster of 54 microRNAs, which we have found to target anti-apoptotic genes, suggesting that dysregulation of this locus contributes to ?-cell failure in type 2 diabetes. Here, we propose to investigate both epigenetic regulation and biological function of this locus in mouse and human ?-cells. In Aim 1, we will investigate the molecular mechanism that causes dysregulation of the MEG3 locus in diabetes. Specifically, we will test the hypothesis that hyper-methylation of a differentially methylated region (DMR) near the promoter of the MEG3 gene causes loss of binding of ?-cell specific transcription factors in an enhancer in the MEG3 gene. In Aim 2, we will determine the specific function of the MEG3 locus in ?-cell physiology and survival using both mouse genetic and innovative human epigenetic inactivation. Multiple biochemical and molecular assays will be performed on MEG3 deficient ?-cells. Together, these experiments will provide important new insights into the molecular etiology of ?-cell failure in type 2 diabetes.